A magnetic resonance imaging apparatus irradiates a radiofrequency magnetic field at specific frequency to a subject placed in a static magnetic field, so as to excite nuclear magnetization of each nucleus of hydrogen or the like contained in the subject and to detect a magnetic resonance signal generated from the subject and thereby acquiring physical/chemical information. In addition to a magnetic resonance imaging (hereinafter abbreviated as MRI) now in widespread use, a magnetic resonance spectroscopic imaging (herein after abbreviated MRSI), which separates magnetic resonance signals to be rendered as images every molecules with a base as to the difference (hereinafter called chemical shift) among resonant frequencies due to the difference among chemical bonds of various molecules including a hydrogen nucleus, is known as a method of imaging using the magnetic resonance imaging apparatus.
By using MRSI, a distribution of metabolite in vivo can be imaged non-invasively. However, a concentration of each metabolite is often very low so that the signal to noise ratio (hereinafter, called SNR) becomes low. Therefore, it is difficult to improve spatial resolution and time resolution. When a signal is measured without water suppression of high concentration upon execution of a MRSI measurement, a weak signal of a metabolite is buried in a skirt of a very strong signal peak generated from water. This makes it difficult to separate and extract a metabolite signal and therefore, a pre-processing for suppressing water signal is performed immediately before execution of usual excitation and detection. The measurement in which the MRSI measurement is performed after a pre-processing for suppressing water signal is called a water-suppressed measurement.
In the MRSI, it is necessary to perform a process called a phase correction in a spectrum-axis direction for calculating image information reflecting concentrations of various metabolites contained in vivo. In the phase correction in the spectrum-axis direction, spectrum signals having chemical shift information are made in phase, where, the spectrum signal is obtained by performing a transformation between a time-component and a frequency-component in a time-axis direction (for example, a Fourier transform), on measured magnetic resonance signal. However, in the MRSI, a low SNR, in measuring metabolite, makes SNR of signals acquired by the water-suppressed measurement low. That results in reducing the phase correction accuracy. There is a technique where, the phase correction in the spectrum-axis direction on a spectrum with low SNR obtained by the water-suppressed measurement is performed, using a phase characteristic calculated from a spectrum with high SNR obtained in the MRSI measurement without a pre-processing for suppressing a water signal (non-water-suppressed measurement) (refer to, a patent document 1 for example).
On the other hand, there is a technique in the recent MRI where an image measurement is performed, using a multi-array coil (MAC), combined multiple surface coils each having a high receiving sensitivity flatly or spatially. Using the MAC, images with high SNR can be obtained by summing obtained multiple images. Also in the MRSI measurement, it is expected to improve the SNR with a usage of the MAC.
Patent document 1
Japanese patent application laid open No. 2001-346779